102 





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ESSENTIALS OF ZOOLOGY 



and the posterior, the post-central ossicle or prepyloric ; and 

 the latter is produced to form the median tooth which lies 

 at the bottom of the depression between the two gastric 

 cavities. On each side of the cardiac is articulated a small 

 curved prelateral ossicle or pterocardiac. Between the pre- 

 lateral and the pyloric on each side, and articulating with the 

 latter through the intervention of a small exopyloric, is the 

 large post-lateral ossicle or zygocardiac, which is bent down- 

 wards into a strong, serrated lateral tooth. The muscles 



Cardiac 

 Prelateral 



Oesophagus 



Precentral 

 Post-lateral 



Accessory 



tooth 

 Lateral 



Post-central with 

 median tooth 



Ophthalmic a. 

 Antennary a. 



'sal ostium 



sal 

 abdominal a. 



Bladder 



Kidney 



Ureter End sac 



FIG. 49. Nephrops. A, gastric mill, ventral view ; B, heart from dorsal 

 side ; C, green gland. 



which put this apparatus into motion are principally a pair 

 which stretch forwards from the cardiac region Df the stomach 

 to the carapace, and a pair which pass backwards from the 

 pyloric region, also to the carapace. When these contract, 

 the lateral teeth are pulled inwards and upwards, and the 

 median tooth at the same time is drawn upwards and back- 

 wards ; and when the muscles are released these movements 

 are reversed. In addition to the sclerites mentioned, two 

 accessory lines may be seen extending forwards and back- 

 wards from the junction of the pre- and the post-lateral on 

 each side. The hinder one ends in a distinct round ossicle 

 bearing two or three small teeth. Setae are developed in 

 relation to a ventral pair enclosing a groove just behind the 

 gullet. Other hardened lines may be distinguished in the 



